One level of tempest cleric gives you all weapons and armour + two types of damage reaction... I mean if you just want it for the unlock I don't see fighter as the best option
Tempest Cleric doesn't get you archery fighting style, of which a +2 to bow/crossbow attack rolls is pragmatically going to matter a lot more than everything that a 1 level dip in Tempest Cleric would provide, especially since you're probably not going to get attacked in melee often enough (or even get hit to begin with) for the damage reaction to matter. You don't want to miss your Sharpshooter shots.
